Processes driving orogenic styles and long-term isostatic versus dynamic support of the topography have been largely debated in domains of plate convergence. The tectonic evolution of orogens reflect the interactions between mantle flow driving plates and the inherited rheology and composition of moving plates. Here we show that the tectono-magmatic evolution of the European lithospheric mantle and structure, which inherits past subduction/collision (e.g. Cadomian, Variscan) and rifting events (Tethys/Atlantic), control first-order crust-mantle coupling, plate-mantle coupling, defining Alpine-type orogens. The lack of thermal relaxation needed to maintain rheological contrasts over several hundreds of millions of years requires high mantle heat flux below Central Europe since at least the Permian. A combination of edge-driven convection on craton margins and asthenospheric flow triggered by rift propagation during the Atlantic and Tethys rifting is suggested to be the main source of heat. Timing and rates of exhumation recorded across Western Europe during the Cenozoic convergence reveal an additional control by the architecture of Mesozoic rifted margins that defined a complex array of small continental blocks with European affinity (e.g. S-Iberia, Ebro/Sardinia-Corsica) caught between the East European and West African cratons, and Adria. By 50 Ma the acceleration of orogenic exhumation, from the High Atlas to the Pyrenees, occurred synchronously with the onset of extension and magmatism in the West European Rift. Extension marks the onset of distinct orogenic evolution between Western Europe (Iberia) and the Alps (Adria) in the east, heralding the opening of the Western Mediterranean. While the details of the Cenozoic topographic history of peri-Mediterranean orogens are understood to be controlled by the rheology and architecture of rifted margins combined with changing large-scale kinematic boundary conditions (e.g. Atlas, Betics, Pyrenees, Alps), their post-10 Ma, quaternary to current surface and tectonic evolution appears to illustrate increasing control by magmatism and flow at the asthenosphere-lithosphere boundary.
The tectonic evolution of the plate boundary between Iberia and Europe since the Variscan and more clearly since the Mesozoic rifting is at the origin of heterogeneities of densities and structure, in the crust and the mantle, which have an impact on the distribution of the current stresses and post-orogenic uplift in the Pyrenees. Here, we investigate the lithosphere structure across the Pyrenees and Western Europe using LitMod2D that integrates geophysical and petrological data sets to produce the thermal, density, and seismic velocity structure of the lithosphere and upper mantle. Of particular interest is the chemical composition of the mantle, including the degree of serpentinization near the North Pyrenean Fault (>10 km), and the shape of the lithosphere-asthenosphere boundary at a larger scale (>100 km). The topography and geophysical constraints, including LAB geometry, Vs, Vp data are well reproduced for a weak fertile Phanerozoic lithosphere. Our results suggest that accounting for serpentinization allows fitting second-order gravity and seismological features in the lithosphere, but not topography which is controlled to first-order by high lateral variability in crustal thickness and lithosphere strength.
ABSTRACT Defining temporal and spatial distribution of shortening is critical to reconstruct past plate motions and to examine mechanical coupling processes at convergent plate boundaries. Understanding the collisional evolution of the British Mountains and Beaufort-MacKenzie basin in the northern Alaska–Yukon region is key for the geodynamics of the Arctic region. With the aim to resolve the exhumation history of this region, we present the first zircon fission-track and (U-Th)/He analyses on apatite and zircon from the Neruokpuk Formation (ca. 720–485 Ma), which forms the orogenic basement of the British Mountains. Zircon fission-track ages show partial resetting, indicating the Proterozoic basement did not reside at temperatures above 240 °C. Thermal modeling of zircon and apatite (U-Th)/He data indicates that our samples reached this maximum temperature at ca. 100 Ma. The onset of the Brookian collision is indicated by exhumation from ca. 80 Ma. A total exhumation of 7–8.5 km since the Late Cretaceous is inferred. Apatite (U-Th)/He ages of ca. 50 Ma show that exhumation was less than 2.5 km since the early Eocene. We infer from a comparison with the temporal evolution of exhumation from adjacent orogenic domains that shortening progressively shifted northward from the British Mountains to the Barn Mountains and offshore in the Beaufort Sea during the Paleocene. Along-strike variations in the architecture of the rifted margin of Arctic Alaska is suggested to have exerted a strong control on the structural styles and observed exhumation patterns.
By demonstrating that extensional inheritance plays a decisive role in the formation of orogens, recent studies have questioned the ability of a unique, complete Wilson cycle model to explain the diversity of collisional orogens. For 5 years, the OROGEN Research Project had therefore the ambition to challenge this classical Wilson cycle model. By focusing on the diffuse Africa-Europe plate boundary in the Biscay-Pyrenean-Western Mediterranean system, the project questioned the preconceived “Orogen singularity” assumption and investigated the role of divergent and convergent maturities in orogenic and post-orogenic processes. This work led us to rethink the development of collisional orogens in a genetic (or process-driven) way and to propose an updated version of the ” classical Wilson cycle”, the Wilson Cycle 2.0, and the ORO-Genic ID concept presented in this paper. The particularity of the Wilson Cycle 2.0 is to take into account the divergence and convergence maturity reached during extensional and orogenic processes in proposing different tectonic tracks associated with different ORO-Genic ID numbers. The ORO-Genic ID is composed of a letter (or track), corresponding to the maturity of divergence reached and a number corresponding to the maturity of convergence reached during the formation of the orogen. This new concept relies on the observed pre- and syn- convergent tectono- stratigraphic and magmatic record and deformation history and can be identified in using diagnostic criteria presented in this paper. It represents therefore a powerful tool that can be used to characterize the evolution and the architectural type of an orogenic system. Moreover, as a mappable concept, it can be easily used worldwide and can help us to explain differences in the style of deformation at crustal scale between orogens.
